Linkages between below and aboveground communities: Decomposer responses to simulated tree species loss are largely additive

Inputs of aboveground plant litter influence the abundance and activities of belowground decomposer biota. Litter-mixing studies have examined whether the diversity and heterogeneity of litter inputs affect decomposer communities in ways that can be predicted frommonocultures. They have mainly attempted to detect non-additive effects of litter mixing, although individual species effects (additivity) as well as species interactions (non-additivity) may alter decomposition rates. To determine potential impacts of plant species loss on aboveground-decomposer linkages, we assessed both additive and non-additive effects of litter mixing on decomposer communities. A full-factorial litterbag experiment with leaves from four deciduous tree species was conducted, to assess responses of bacteria, fungi, nematodes, and microarthropods. Data were analyzed using a statistical method that first looked for additive effects based on the presence or absence of species and then any significant species interactions. We observed almost exclusively additive effects of all four litter species on decomposer biota, with each species exerting effects on different aspects of the community. These results imply that the consequences of species loss for the decomposer community will be largely predictable from knowledge of single species litter dynamics. The two species at opposite ends of the quality spectrum exerted the most effects. Highquality Liriodendron tulipifera supported a more diverse arthropod community and drove bottom-up effects on the decomposer food web. Low-quality Rhododendron maximum had negative effects on most groups of biota. Litter of mid-quality species exerted fewer effects. The influence of litter species richness on the Tylenchidae (nematodes) was the only non-additive effect of litter mixing. Together, these data demonstrate an effect of plant community composition on decomposer biomass, abundance, and diversity, confirming a link between above and belowground communities. We were able to identify the species to which the decomposer community is most sensitive, aiding predictions of the consequences of the loss of these dominant species on the decomposer community, with potential feedbacks for organic matter and nutrient turnover. 2009 Elsevier Ltd. All rights reserved.